1. Technical Field
The present invention relates to a lane keeping assist system (LKAS).
2. Related Art
With the improvement of various functions of vehicles, various technologies for improving the safety and comfort of the drivers and passengers have been introduced. In particular, an LKAS capable of keeping a vehicle in a particular lane is close to commercialization.
An LKAS is a system for detecting whether a vehicle deviates from a target lane and assisting a driver in remaining in the target lane at a desired speed. In order to implement this, the target lane and the kinematic characteristics of the vehicle must be measured in real time, and appropriate control must be performed based on the results of the measurement.
In a prior art LKAS, the video data processing speed of a video sensor is lower than the data processing speed of the LKAS. Because of this, the prior art LKAS does not perform the function in a reliable manner.
For example, when the data processing period of the system is 10 ms and the video data frame measurement period of the video sensor is 50 ms, the system receives new video data from the video sensor every 50 ms in the processing of data, and thus the system repeatedly uses previous video data for 40 ms (four periods). As a result, the system has a problem in that the system cannot appropriately control the traveling of a vehicle because the same video data is used for five instances of data processing.
Of course, in the case of a high-performance video sensor, the data processing speed thereof can be synchronized with the data processing speed of a system, and thus the lane keeping function may be improved. However, since the high-performance video sensor is expensive, the use of the high-performance sensor increases manufacturing costs.
FIG. 1 is a diagram showing variables indicative of the kinematic characteristics of a vehicle. Referring to FIG. 1, the control variables of a lane keeping assist system that must be taken into account when a vehicle travels along a curved lane will be described below.
An LKAS enables a vehicle to remain in a lane the vehicle is traveling by measuring or estimating a velocity V of the vehicle, a lateral velocity ν, a yaw rate γ, a required forward angle δf and a slide slip angle β, a deviation angle θp at a measuring point, and a deviation distance yp at the measuring point, outputting a steering motor torque based on the results of the measurement or estimation, and transmitting a drive signal related to the torque to the steering motor.
FIG. 2 is a graph illustrating the lane following performance of the prior art LKAS, and FIG. 3 is a graph illustrating the lane following performance based on video detection speeds of the video sensor of the prior art LKAS.
Referring to FIG. 2, a problem arises in that the system cannot follow the traveling characteristics of a vehicle in real time due to the repeated use of data that is measured by the video sensor. Accordingly, the vehicle controlled by the system cannot be accurately kept in its lane and has a certain error value.
FIG. 3 shows that an error in the deviation distance (e.g., approximately 10 cm) may occur when the data processing period of a video sensor is 50 ms and the data processing period of a system is 10 ms.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.